Catalytic oxidation of ammonia

ABSTRACT

This invention relates to the catalytic oxidation of ammonia. The catalytic compounds are complex catalysts with limited porosities, with specific surface areas between 0.02 and 2 m2/g. containing an active material bonded by ceramic-type bonds to the elements of a refractory carrier made of refractory oxides such as magnesia, zirconia, silica. Such compounds are suitable for the oxidation of ammonia over fixed beds or fluidized beds.

United States Patent Senes et al.

[451 Dec. 16, 1975 CATALYTIC OXIDATION OF AMMONIA Inventors: Michel Senes, Saint Nazaire; Pierre Lhonore, Douai; Michel Pottier, Saint Nazaire; Jacques Quibel, Maisons Laffitte, all of France Societe Chimique de la Grande Paroisse et Produits Chimiques, Paris, France Filed: Mar. 28, 1973 App]. No.: 345,685

Related US. Application Data 112,879, Feb. 5, 1971,

Assignee:

Division of Ser. No. abandoned.

Foreign Application Priority Data Feb. 9, 1970 France 70.04454 US. Cl. 252/456; 252/460; 252/472; 252/473; 423/404 Int. Cl. ..B01J 29/16; B01J 29/12; COlB 21/26 Field of Search 252/457, 460, 472, 473, 252/456; 423/402-404 References Cited UNITED STATES PATENTS 11/1919 Classen 23/162 1,680,807 8/1928 Schultze 252/473 1,771,130 7/1930 Larson 252/473 X 2,106,597 1/1938 Ferguson 252/473 X 2,167,708 8/1939 Carter et al 423/403 2,467,446 4/1949 Smithells 423/404 2,639,223 5/1953 Shapleigh 252/457 X 3,267,045 8/1966 Isack, Jr. et al. 252/473 3,565,830 2/1971 Keith et a1. 252/473 X Primary ExaminerCarl F. Dees Attorney, Agent, or Firm-Browdy and Neimark 8 Claims, 4 Drawing Figures US. Patent Dec. 16, 1975 Sheet 1 of2 3,926,853

i I I b 5.000 I0.0CO 15-000 20.000 VVH FIG. I

500 e'oo 1'00 e'oo T "c FIG. 2

U.S. Patent Dec. 16, 1975 Sheet2of2 3,926,853

IOO.-

FIG. 3

FIG. 4

This invention relates to the catalytic oxidation ofarnmonia to nitrogen oxides, notably nitrogen monox' ide, for the production of, nitric acid. The nitric acid industry habitually uses a catalyst made of pure platinum, or of mixtures of pure metals of the platinum group, as gauzes with wire thicknesses between a few hundredths and a few tenths of a millimeter. 7

It is well known that in the low-temperature range, selectivity must intervene to favor the formation of NO and N rather than N while in the high-temperature range, selectivity must intervene to favor the formation of NO rather than N 0 and N When using the known catalytic technique, the difficulty is to vary the selectivity, owing to the use of a catalyst with a very low thickness (thickness of the gauzes). For instance, with a reactor of 3 m diameter working at low pressure, the total thickness of the gauzes varies between a fraction of a millimeter and a few millimeters.

Besides, metal gauzes catalystsstart losing their activity in a comparatively short time. The replacement, repair and regeneration of conventional catalysts involve costly down-time. 7

It has also been suggested that a catalytic metal or alloy of metals of the platinum group be deposited asa thin, continuous or quasi-continuous layer upon the surface of the flow ducts and the surface macropores of a porous and inert refractory structure.

Depositing a thin layer does not avoid the disadvantages due to lack of selectivity.

On the other hand, the dispersion and the structure of the active material, the nature of the carrier and its intimate bonding with the said active material, the promoters and the porosity have been found to be important factors for catalysis. Such factors cannot be varied, nor introduced simultaneously into a metal or a catalytic metal alloy. t

According to this invention, selective catalytic compounds have been discovered which are thermally, mechanically and structurally stable, and which have high hardness and resist attrition.

The novel catalytic compounds have such'thermal stability that their use at high temperatures (8001000C) is possible without change of structure or loss of mechanical strength.

At low temperatures (500-300C), the catalytic compounds show high hardness .and resist attrition, which allows their preferential use in fluidized beds with outstanding results.

The novel catalytic compounds according to the invention have a special structure of the crystals unit cells which contains a great number of oxygen atoms, thus giving them special properties as catalysts.

On the other hand, the catalytic compounds according to the invention also have the advantage of making it possible to treat much larger flow rates of ammonia,

with the same amount of active material, than with' Conventional platinum gauzes. The flow rates can be about 12 times larger than the usual ones. Moreover, the temperatures of treatment is about 100C lower than with platinum gauzes.

The novel catalytic compounds make it possible to use very high volume rates, notably with stationary beds, while effecting the oxidation reaction within a very wide range of pressures, with. satisfactory yields at high pressures.

The catalytic compounds of. the invention are complex catalysts with limited porosities and specific surface -areas between,0.02 and 2 m /g, containing an active material bonded by ceramic-type bonds to the elements of a refractory carrier made of refractory oxides, such as magnesia, silica and zirconia.

According to one embodiment of the invention, the active material of the said complex catalysts is a metal of the platinum group, in amounts between 0.1% and 10%, preferably between 0.5% and 4%.

According to a favorable variation of the invention, the metal of the platinum group is associated with metal oxides or promoters such as the oxides of iron,

' nickel, cobalt, titanium, vanadium, bismuth and molybdenum.-

It has been found that the use as promoters of metal oxides, notably of magnetite Fe O of vanadium pentoxide V 0 of cobalt oxide CoO, of nickel oxide NiO,

bismuth oxide and hematite'Fe O gives a special structure of the unit cell which contains a great number of oxygen atoms, and presumably has a favorable catalytic effect on the oxidation reaction.

The catalytic compounds in which the active material, in: small amounts, isvery intimately combined with;

the remainder of the carrier, mainly by ceramic-type bonds, may contain no platinum or metals of the platinum group. In such compounds the active material ismade of one or several metal oxides known as promot- The content of C00 is 4% to 20%, preferably 12 I, The content of bismuth oxide is 4%, to 20%, preferably about 12%. The content of molybdenum is 4% to 20%, preferably about 16%. The refractory oxides, introduced separately or simultaneously, have the followingcontents in the com-,

pounds:

Magnesia MgO: 10% to preferably 40% to 50%. Silica SiO 0.2% to 10%, preferably about 8%. Zirconia ZrO 5% to 50%, preferably about 30%. The complex catalysts with limited porosities according to the invention are prepared by sintering at high temperatures (1300C or higher), thus forming solid solutions.

Prior to sintering, the components of the catalysts are uniformly mixed, then compressed at pressures in the 1,00010,000 bar range.

Due to this special method of preparation, the various components of the compound are combined into solid solutions.

The catalytic compounds of the invention are notably suitable for the oxidation of ammonia on stationary beds. The results are especially satisfactory when a mixture of ammonia and air containing 5% to 14% ammonia by volume is led, with very high volume rates (between 10,000 and 500,000 Nl/h per liter catalyst), under absolute pressure between 1 and 60 bars, with an 3 initial temperature around 150C, over a compound such as described above.

According to a variation of the method, the air in the mixture is enriched with oxygen.

4 The NH air mixture is preheated to 150C. At the outlet, the gases are converted to HNO and the results are expressed as converted ammonia.

The results of this test on a stationary bed are shown The use of the said catalytic compounds in stationary 5 on Table I hereafter.

P pressure IT inlet temperature HT halfway temperature OT outlet temperature.

beds makes it possible to use tubes with small diameters instead of the conventional reactors.

The mechanical strength and high hardness of the The NH /Pt ratio expresses the kg/h ammonia introduced per kg platinum in the catalyst.

VvH expresses volumetric speed ratio of flow gasecatalytic compounds make them especially valuable for 0115 mixture NH air NlH to volume of catalyst exthe catalytic oxidation of ammonia on stationary beds.

The fluidized-bed method is carried out under pressures which can reach 60 bars. The reaction mixture is introduced into a compound according to the invention pressed in liter.

The yield as the percent ammonia converted to nitric acid.

As a comparative test, Table 'II hereafter shows the under the shape of particles with sizes between 60 and results obtained under the best practical conditions on 25014., at temperatures between 500C and 800C, the

platinum gauzes.

TABLE II NH /Pt NH by P Temperature of gas mixture Temperature Yield volume bars Inlet Outlet of platinum C C gauzes C volume rate on the fluidized bed being 3,500 to 20,000 40 A parallel between test n 7 on Table l and the test on Nl/h per liter catalyst. The amount of ammonia in the mixture is 5% to 14% by volume. The air may be oxygen enriched.

The following illustrative examples do not limit the scope of the invention.

EXAMPLE I.

A catalyst is prepared by intimately mixing the components, compressing the mixture to about 1,000 bars, then sintering at high temperature, between 1300C and 1400C, so as to get the following formulation by weight:

Compound A:

M0 8.5 zro 31.7 MgO 49.5 v 0 0.9 sio 8.6 Pt 0.7

Table II shows that catalytic compound A according to the invention makes it possible to treat, with the same amount of platinum, a flow rate 1,560/133 l 1.7 times higher than with conventional platinum screen gauzes.

On the other hand, the temperature is lower by about FOOC with the catalyst according to the invention than with conventional platinum gauzes.

EXAMPLE 2.

A catalyst without platinum or metals of the platinum group is prepared by mixing and shaping the components, then by sintering at 1300C or higher, so as to obtain the following formulation: Compound B:

NiO V 0 MgO ZrO SiO, Fe 0,

Compound B is tested in the same reactor as in Ex. 1. The results of this stationary bed test are summarized on Table 111.

TABLE 111 No vol/vol/h NH by P Temperature of gas mixture yield volume bars 1T H'l OT 7:

C "C C TABLE Ill-continued No vol/vol/h NH;,by P Temperature of gas mixture yield volume bars IT HT OT C "C C I NH air as mixture. The reactor includes a heat EXAMPLE 3 3 g Catalytic compound C is prepared under the same conditions as in Ex. 1 and Ex. 2. Compound C:

exchanger for evacuating the calories from the reaction.

The results of the test are shown on Table VI hereafter.

C00 12 VI V205 LO TABLE Mgo No VvH NH by P Temperature of Yield Z502 29 volume bars fluidized bed, s10 8 0 Fe,0, 7.9

1 3,500 9.6 1 750 71 2 5,000 9.6 1 750 73 Compound C is tested in the same way as in Ex. 1. 3 3.338 3.2 i 328 3% Table IV hereafter summarizes the conditions and 5 121000 750 95 results of the test. 6 17.000 9.6 1 750 96 7 20,000 9.6 1 750 96 TABLEIV No VvH 70 Nl-l by P Temperature of gas mixture Yield volume bars lT HT OT "C C C EXAMPLE 4 This example is given as a comparative test.

The catalyst is prepared differently from Ex. 1.

Alumina is impregnated with a solution of tetrachloroplatinic acid in such a way that after treatment at 900C, there remains 2% platinum deposited on the carrier. The specific surface area of the catalyst is 86.5 mZ/g; the average diameter of the pores is 92 A.

Catalyst D of this example is tested under the same conditions as in Ex. 1. The results are shown on Table V hereafter.

FIG. 1 of the appended drawing shows the yield of ammonia vs. the volume rate (vol/vol/h). The volume rates (abscissae) are in Nl/h, the yields (ordinates) in It should be noticed that the yields reach highly desirable values from volume rates of l0,000 Nl/h upwards.

EXAMPLE 6 Comparative tests on fluidized beds with catalytic TABLE V No 7: NH by VvH P Temperature of gas mixture Yield volume bars [T T OT "C "C "C A parallel with the results of the tests in Ex. 1 shows the comparatively low yields obtained in this test.

The high platinum content of catalyst D (2% instead of 0.7% for catalytic compound (A) clearly shows that platinum is not the only active element in the catalysis of the oxidation reaction of ammonia.

EXAMPLE 5 Into a fluid-bed reactor is introduced catalytic com pound A of Ex. 1, previously screened to the proper particle size to allow fluidization at the flow rate of the 7 8 TABLE v11 TABLE lX-continued No Compound A Compound D Pressure bars Yield Temperature of Yield Temperature Yield 48 gl fluidized bed "c fluidized bed C 6O 98 1 525 75 528 43 2 565 85 560 48 i 238 3; 2 ,8 20 The outstanding behavior of the catalyst should be 5 94 55 noticed. The yields (as NI-I converted) are qu1te attractive, even under high pressures. These results are shown on curve 3, FIG. 4 of the The Parallel clearly Shows the Superlonty of appended drawing, on which the yields are the ordipound A according to the invention over a catalyst w1th mates and the pressures are the abscissae high platinum content deposited as a continuous layer on an inert carrier, in the case of a fluidized bed. EXAMPLE EXAMPLE 7 Catalytic compound E is prepared under the same cond1t1ons as 1n Example 1 and Example 2. In this example, the behavior of the catalyst 1n a stationary bed is investigated under various pressures, the yields being expressed as NH converted. Compound E:

In the following series of tests, the results of which 8 are shown on Table VIII, the volume NI-I is 9.6, the 26 411 volume rate is 200,000 Nl/h, and the temperature is gig: Z2

l controlled 1n the same way, the outlet temperature 6 99% being 875C.

TABLE VIII Compound E 1s tested in the same way as in Example Pressure Yield 1 I bars Table X hereafter summarlzes the condltlons and 32 results of the test. i3 32 TABLE x N VvH NI-l by P Temperature of gas mixture 1T HT OT Yield volume bars 'C "C "C What we claim is: l. A stable catalytic composition for the catalytic v oxidation of ammonia to nitrogen oxides, comprising: i 3 i 3 of z ffii drawmg g i a complex catalyst of limited porosity, containing no 8 6 i presslrg 2 gressures (a members of the platinum group, with a specific 2 3 as an 5 e y le S (or ma es) are expresse surface area of between 0.02 and 2 'm /g, 3 zf h f h I t h M b said catalyst consisting essentially of metallic oxides ggf l e o t e i i S .i e consisting of iron oxide, vanadium oxide and at 3 g o z g i least one further metallic oxide selected from the fi g. a s f O f f fi ewl group consisting of oxide of nickel, cobalt and a Sma lameter W 10 can W1 S n lg pressures bismuth, and a refractory material consisting of EXAMPLE 3 magnesia, silica, zirconia or a mixture thereof, all combined by mixing the powdered constituents, In thls example the are made on h fluldlze.d compressing at 1,000- 10,000 bars and sintering at bed of Ex. 5 under various pressures w1th catalyt1c 6 d A 1300 C or hlgher. 1 q f n 2. A catalyst in accordance with claim 1 wherein the 7 gf 1 101115 3 0 contents by weight of said metallic oxides, when presi g N'l/h 6O ent in said composition, are from 0.5 to 20% for Fe O I? v0 fl b 750C from 9 to 80% for Fe O from'0.5 to 10% for V 0 and z 0 S f tabl IX h re ft from 4 to 20% for NiO, C00 and bismuth oxide.

6 resu S are ummanze on e e 8 3. A catalytic composition in accordance with claim TABLE IX 1 wherein the contents by weight of said refractory pressure has Yield 65 material in compound are 10 MgO, 0.2

10% S10 and 5 50% ZrO 3g A stable catalytic composition for the catalytic 35 93 oxidation of ammonia to nitrogen oxides, comprising:

9 a complex catalyst of limited porosity with a specific surface area between 0.02 and 2.0 m /g, said catalyst consisting essentially of 0.1 to 10% of an active material selected from the group consisting of the metals of the platinum group, and a refractory oxide carrier comprising, in the composition, l-60% MgO, 02-10% SiO and 5'-50% ZrO said active material being intimately combined in solid solution with said carrier by ceramic-type bonds formed by mixing said active material and said carrier, compressing at 1,000 to 10,000 bars pressure and sintering at a temperature of at least 1300C.

5. A stable catalytic compound according to claim 4, wherein the metal of the platinum group is associated with a metal oxide of the group consisting of oxides of iron, nickel, cobalt, titanium, vanadium, bismuth and molybdenum.

6. A stable compound according to claim 4, wherein the metal of the platinum group is associated with a metal oxide of the group consisting of: oxides of iron, the content of which being from 0.5 to 20% for Fe O and 9 to for Fe O oxides of nickel, the content of which being from 4 to 20% for M0; oxides of bismuth and molybdenum, the content of which being from 4 to 20%; oxides of cobalt the content of which being from 4 to 20% for CO0; and oxides of vanadium the content of which being from 0.5 to 10% for V 0 7. A catalyst in accordance with claim 4 wherein said metal is present in said composition in an amount of 0.5 4%.

8. A catalyst in accordance with claim 5, wherein said magnesia is present in about 40 to 50%, said silica is present in about 8% and zirconia is present in about 30%. 

1. A STABLE CATALYTIC COMPOSITION FOR THE CATALYTIC OXIDATION OF AMMONIA TO NITROGEN OXIDES, COMPRISING: A COMPLEX CATALYST OF LIMITED POROSITY, CONTAINING NO MEMBERS OF THE PLATINM GROUP, WITH A SPECIFIC SURFACE AREA OF BETWEEN 0.02 AND 2 M2/G, SAID CATALYST CONSISTING ESSENTIALLY OF METALLIC OXIDES CONSISTING OF IRON OXIDE, VANADIUM OXIDE AND AT LEAST ONE FURTHER METALLIC OXIDE SELECTED FROM THE GROUP CONSISTING OF OXIDE OF NICKEL, COBALT AND BISMUTH, AND A REFRACTORY MATERIAL CONSISTING OF MAGNESIA, SILICA, ZIRCONIA OR A MIXTURE THEREOF, ALL COMBINED BY MIXING THE POWDERED CONSTITUENTS, COMPRESSING AT 1,000-10,000 BARS AND SINTERING AT 1300*C OR HIGHER.
 2. A catalyst in accordance with claim 1 wherein the contents by weight of said metallic oxides, when present in said composition, are from 0.5 to 20% for Fe3O4, from 9 to 80% for Fe2O3, from 0.5 to 10% for V2O5 and from 4 to 20% for NiO, CoO and bismuth oxide.
 3. A catalytic composition in accordance with claim 1 wherein the contents by weight of said refractory material in said compound are 10 - 60% MgO, 0.2 - 10% SiO2 and 5 - 50% ZrO2.
 4. A STABLE CATALYTIC COMPOSITION FOR THE CATALYTIC OXIDATION OF AMMONIA TO NITROGEN OXIDES, COMPRISING: A COMPLEX CATALYST OF LIMITED POROSITY WITH A SPECIFIC SURFACE AREA BETWEEN 0.02 AND 2.0 M3/G, SAID CATALYST CONSISTING ESSENTIALLY OF 0.1 TO 10% OF AN ACTIVE MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE METALS OF THE PLATINUM GROUP, AND A REFRACTORY OXIDE CARRIRE COMPRISING, THE COMPOSITION, 10-60% MGO, 0.2-10% SIO2, AND 5-50% ZRO2, SAID ACTIVE MATERIAL BEING INTIMATELY COMBINED IN SOLID SOLUTION WITH SAID CARRIER BY CERAMIC-TYPE BONDS FORMED BY MIXING SAID ACTIVE MATERIAL AND SID CARRIER, COMPRESSING AT 1,000 TO 10,000 BARS PRESSURE AND SINTERING AT A TEMPERATURE OF AT LEAST 1300*C.
 5. A stable catalytic compound according to claim 4, wherein the metal of the platinum group is associated with a metal oxide of the group consisting of oxides of iron, nickel, cobalt, titanium, vanadium, bismuth and molybdenum.
 6. A stable compound according to claim 4, wherein the metal of the platinum group is associated with a meTal oxide of the group consisting of: oxides of iron, the content of which being from 0.5 to 20% for Fe3O4 and 9 to 80% for Fe2O3; oxides of nickel, the content of which being from 4 to 20% for NiO; oxides of bismuth and molybdenum, the content of which being from 4 to 20%; oxides of cobalt the content of which being from 4 to 20% for CoO; and oxides of vanadium the content of which being from 0.5 to 10% for V2O5.
 7. A catalyst in accordance with claim 4 wherein said metal is present in said composition in an amount of 0.5 - 4%.
 8. A catalyst in accordance with claim 5, wherein said magnesia is present in about 40 to 50%, said silica is present in about 8% and zirconia is present in about 30%. 